Turbo size on TD engines

MMamdouh · Post by **MMamdouh** » Mon Jan 22, 2007 12:35 pm

i have seen somme diesel that are turboed and i couldn't help noticing that the turbo on those cars are relativly small compared to the ones usualy on petrol engines... why is that?

is it because the diesel engine doesn't rev that high so it has much lower CFM that any petrol engine so the air supply it needs is about half what a standard petrol engine would need??

MMamdouh

exist3nce · Post by **exist3nce** » Mon Jan 22, 2007 7:27 pm

I have noticed the same thing...... extremely small turbos on diesel motors. I'm not entirely sure why, but I would think it is because of it being naturaly low revving....... so you would want boost right away almost off idle. Also diesels have more alot more torque than hp usually which ends up giving you really good low and mid but poor top end. (At least this is what I notice when I drive VW TDI golf/jetta). So I guess the turbo is just sized to the characteristics of the motor.

MMamdouh · Post by **MMamdouh** » Mon Jan 22, 2007 9:19 pm

well... you are right as far as the amout of torque a diesel engine produce and indeed it lacks HP at top end and thats why those engines make use of a turbo.

the point it - in my opinion - is that the top end of a diesel engine is something arround 4000 ~ 4500 RPM so the amount of exhaust exiting as well as the amout of air entring the engine at diesel top end revs is almos half what a petrol engine suck/produce when it is revving at 7000 RPM... this is the only logical explanation i could get.

can someone provide any more feedback/info on this??

MMamdouh

klonek78 · Post by **klonek78** » Mon Jan 22, 2007 9:32 pm

diesel engines needs about 30-35% more air to produce the same HP according to petrol engines.... usually they produce higher boost also. on the other hand diesel engines doesn't rev above 4500rpm and that's why diesel turbo has different turbo/compressor ratio than petrol one.

MMamdouh · Post by **MMamdouh** » Fri Jan 26, 2007 1:19 pm

forgot to say that so many of them setups got no WG... is it because the turbo doesn't put too much pressure in the first place due to the fact it never spins that fast because of the low revving engine it is hooked up to??

MMamdouh

klonek78 · Post by **klonek78** » Fri Jan 26, 2007 3:59 pm

turbo in diesel engine is able to produce more (higher) pressure but less flow.

MMamdouh · Post by **MMamdouh** » Sat Jan 27, 2007 4:21 pm

i am lost....

whats the difference between pressure and flow? or in other words what does flow got to do with boosted applications? doesn't the WG open at certain "pressure" rather than certain "flow"?

how can flow be a deciding factor on wether to have a WG or not?

MMamdouh

Nubira2.2 · Post by **Nubira2.2** » Sat Jan 27, 2007 4:26 pm

simple if you have 2 hoose

one is 1" diameter and the other 3" diameter

both can hold ... lets say ... 10psi

but the 3" one can flow a lot more of ... lets say water than the 1" @ the same pressure

MMamdouh · Post by **MMamdouh** » Sat Jan 27, 2007 4:37 pm

ok... i know the physical difference between both terms but what i am not getting is why you don't need WG on a TD if it doesn't give so much flow yet it produces as much pressure as the turbo on a pertol engine?

as far as i know the WG opens at a certain pressure so given the fact that petrol and diesel engines run turbos to almost same pressure then you need to control that pressure... right?

or is it just the fact that you are controling the flow in terms of pressure so at say... 10 psi you are getting enough flow for the petrol engine and you can't go over that but on the diesel 10 psi is not that dangerous flow so you won't need a WG?

sorry i am asj\king too much but i am really lost here.

MMamdouh

exist3nce · Post by **exist3nce** » Sat Jan 27, 2007 7:15 pm

Are you 100% sure that TDIs don't have WG? If they don't I would like to know why as well. My best guess would be because of the low revs = less flow, the turbo would never get into an overboost condition or spin too fast. But this is just a guess.......... anyone here whos sure ?

klonek78 · Post by **klonek78** » Sat Jan 27, 2007 10:13 pm

MMamdouh wrote:ok... i know the physical difference between both terms but what i am not getting is why you don't need WG on a TD if it doesn't give so much flow yet it produces as much pressure as the turbo on a pertol engine?

as far as i know the WG opens at a certain pressure so given the fact that petrol and diesel engines run turbos to almost same pressure then you need to control that pressure... right?

or is it just the fact that you are controling the flow in terms of pressure so at say... 10 psi you are getting enough flow for the petrol engine and you can't go over that but on the diesel 10 psi is not that dangerous flow so you won't need a WG?

sorry i am asj\king too much but i am really lost here.

MMamdouh

you can use small turbo without WG even on petrol engines

these turbos are very small and their main purpose is to improve torque not HP. try to put something like GT12 in over 2.0liter engine - you won't get more power (probably less

) but your torque will be great at low rev. in this case WG won't be necessary because GT12 won't produce enough FLOW in 2liter engine to reach high boost

exist3nce · Post by **exist3nce** » Sat Jan 27, 2007 10:30 pm

some further interesting reading on TDI motors...

http://tdiclub.com/TDIFAQ/

klonek78 · Post by **klonek78** » Sat Jan 27, 2007 10:34 pm

exist3nce wrote:some further interesting reading on TDI motors...

http://tdiclub.com/TDIFAQ/

all TDI, HDi etc has WG or VNT (Variable Nozzle Turbo) - "non WG" turbos were used in older diesel engines.....

MMamdouh · Post by **MMamdouh** » Sun Jan 28, 2007 8:16 am

thank you all for the clarification.

MMamdouh

Daewice · Post by **Daewice** » Tue Mar 27, 2007 6:36 pm

I disconnected the W/G on my 2.5 TDi Pajero. Now I get up to 17psi instead of the 10-11 psi with W/G connected. That doesn´t give me much more power unless I increase the amount of fuel also. But what you don´t get with more boost on diesel, as opposed to petrol, is detonation. Just give it all the boost the turbo can handle and control the amount of fuel. What limits you is the resulting EGT. So in diesels you don´t worry about lean mixture but too rich mixture that produces more heat. (This applies if you have a relatively small turbo. If I had some mammoth turbo I would need a W/G no matter what.)

My 2cents anyway. Hope it makes sense.

Regards from the land of Ice.

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Turbo size on TD engines

Turbo size on TD engines

Turbo TDi